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Alternative aviation fuels and their approval process contribute to one of the biggest challenges in deployment of an enhanced volume of aviation fuels. One of the approved fuel blending components is hydroprocessed esters and fatty acids (HEFAs) for mixing with petroleum-derived fuel (Jet A/A-1) up to 50 vol %. As the ASTM fuel specification (D7566) is merely based on the performance expected, the final blend concentration of HEFA in Jet A/A-1 can vary depending on the resultant fuel properties. Currently, there is a lack of information on how these properties are affected by the constituent chemical composition. The aim of this study was to compare three HEFAs sourced from different feedstocks (camelina, tallow, and mixed fat) and their blends with Jet A (10–60 vol %) based on the detailed chemical composition. The chemical composition was obtained using two-dimensional gas chromatography with mass spectrometry and flame ionization detector. The properties of interest were the distillation profile, density, viscosity, flash point, freezing point, and net heat of combustion. The key observation was that the distillation profile had the main impact on the final fuel properties. Additionally, the selection of the feedstock or the process conditions yielding an end HEFA composition can adversely affect properties, such as viscosity and/or freezing point.

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One challenge in the deployment of alternative aviation fuels is the lengthy “fuel approval process”, which costs millions of dollars and can take many years as the exact effect of these alternative options on engine and framework is still an unknown. A candidate aviation fuel needs to pass the tests as deemed necessary by the ASTM D4054 Standard Practice. The fuel manufacturer faces the risk of not receiving the ASTM certification after significant financial and time investment, which currently acts as a considerable hindrance to broadening the alternative aviation fuel options in commercial and military aircraft. Approval tests are based on the fuel properties and fuel performance as there is currently a knowledge gap on fuel chemical composition–property correlations. Therefore, the aim of this study was to accomplish the first step in this target, i.e., to obtain a detailed chemical composition of four approved blending components (FT-SPK, HEFA, SIP, and ATJ) and their mixtures with Jet A using GC × GC-TOF/MS and GC × GC-FID. Infrared spectroscopy and principal components analysis were utilized as additional techniques to demonstrate the differences among the blending components and Jet A, further utilizing their infrared spectral features. Moreover, the main physiochemical properties were measured, such as distillation profile, density, viscosity, flash point, freezing point, and net heat of combustion. Lastly, the impact of the differences in chemical composition on these main fuel properties was discussed.

The composition of Navy Jet fuel JP-5 was determined using gas chromatography­(GC)-electron impact mass spectrometry and GC × GC/(flame ionization detection) to contain by mass 21% linear alkanes, 29% cycloalkanes, 32% isoalkanes, and 18% aromatic compounds. Various quaternary mixtures of n-dodecane, n-butylcyclohexane, n-butylbenzene, and 2,2,4,4,6,8,8-heptamethylnonane were prepared as possible surrogates for this jet fuel and analyzed for density and viscosity (253 to 333) K, speed of sound (288 to 333) K, surface tension (294 ± 1 K), and flashpoint. Deviation cutoffs for “matching” the JP-5 based on previous studies and fuel specification were ±1.7% for density, ±1% for speed of sound, ±3.5% for bulk modulus, ±2.6% for viscosity, ±2.2% for surface tension, and ±10% for flash point (minimum of 333 K). Seven quaternary mixtures met these cutoffs. Three had compositions that were comparable to the JP-5 and would be good candidates for engine testing. All mixture excess molar volumes showed a trend of increasing to a maximum and then decreasing as the concentration of n-butylbenzene increased. Viscosity deviations ranged from (−0.03 to −0.48) mPa·s.

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